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Design007-Jun2018

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JUNE 2018 I DESIGN007 MAGAZINE 55
ing time of a curing material. For example, if
the product quickly becomes touch dry, it may
not be suitable for stencil printing as the cured
product may block the screen. In most cases, a
minimum amount of material must be applied
for thermal interface and gap filling applica-
tions to ensure maximum heat transfer. For a
thermal interface, the layer must achieve uni-
form coverage over the entire interface; and
when using a gap filler, the material must be
applied while ensuring that all air is expelled,
as air is a poor conductor of heat and may
cause additional hotspots.
If an encapsulation resin is deemed to be
the best choice, it is likely that the entire PCB
will need to be covered. The amount of resin
applied will have to strike a balance between
achieving the desired protection level and min-
imising any weight and volume gains contrib-
uted by the resin.
Hopefully, the foregoing has provided a
useful introduction to thermal management
materials. Look out for my next contribution,
where I will continue exploring thermal man-
agement.
DESIGN007
Jade Bridges is global technical
support manager for Electrolube Ltd.
Superconductors contain tiny tornadoes of supercur-
rent, called vortex filaments, that create resistance when
they move. This affects the way superconductors carry a
current.
But a magnet-controlled "switch" in superconductor
configuration provides unprecedented flexibility in man-
aging the location of vortex filaments, altering the proper-
ties of the superconductor, according to a new paper in
Nature Nanotechnology.
"We work on superconductors and how to make them
better for applications," said Boldizsár Jankó, professor
in the Department of Physics at the University of Notre
Dame and co-corresponding author on the paper. "One of
the major problems in superconductor technology is that
most of them have these filaments, these
tiny tornadoes of supercurrent. When
these move, then you have resistance."
The collaborators' solution overlays
the superconductor with an artificial spin
ice consisting of an array of interacting
nanoscale bar magnets. Rearranging the
magnetic orientations of those nano-bar
magnets results in a real-time rearrange-
ment of the pinning on the superconduct-
ing site. This makes possible multiple,
reversible spin cycle configurations for the
vortices. Spin is a particle's natural, angu-
lar momentum.
"The main discovery here is our ability to reconfigure
these spinning sites reversibly and instead of having just
one spin cycle configuration for the vortices, we now have
many, and we can switch them back and forth," Jankó said.
Because the control of the quantum fluxes is difficult
to visualize in an experiment, simulations were required
to successfully reproduce the results, said Xiaoyu Ma, a
doctoral student in the Department of Physics who con-
ducted the computer simulation in the study and is the
co-first author on the paper. The simulations allowed
researchers to see the detailed processes involved. "The
number of vortex configurations that we can realize is
huge, and we can design and locally reconfigure them site
by site," Ma said. "This has never been realized before."
Designing a Better Superconductor with Geometric Frustration